A lactone is a cyclic compound containing an ester group in the ring, and those having 3, 4, 5, 6 and 7 ring members are referred to as α-, β-, γ-, δ- and ε-lactones, respectively. Many strategies are known for synthesis of lactones, including those using an acid catalyst to synthesize γ-butyrolactones from 4-hydroxybutyric acids, as well as those involving, e.g., reduction of succinic anhydrides or heating of 4-halogenated butyric acids to synthesize γ-butyrolactones.
However, although depending on the types of γ-butyrolactones to be produced, most of these strategies are associated with problems such as formation of byproducts, low yield, risks of explosion, and difficult synthesis of starting materials. Thus, there has been a strong need to develop a novel synthesis method.
To produce 3-hydroxy-γ-butyrolactones by organic synthesis, for example, glycidol and carbon monoxide may be reacted at elevated temperature and pressure in the presence of a noble metal catalyst (U.S. Pat. No. 4,968,817), or 3-butenoic acid may be epoxidized by treatment with hydrogen peroxide in the presence of a platinum catalyst and then hydrated and converted into a lactone (Angew. chem., Int. Ed. Eng 994-1000 (1966)). However, these methods are associated with increased risks of explosion, etc. Also known are a 7-step process starting with L-ascorbic acid or D-isoascorbic acid (Synthesis 570-572 (1987)) and a 3-step process starting with L-malic acid (JP-A-6-172256). However, these processes require complicated procedures and also fail to produce successful results in terms of yield because they involve multi-step reactions.
In addition, 3-hydroxy-γ-butyrolactones are known to be produced by biological processes using Pseudomonas or Enterobacter bacteria as a microbial catalyst to produce (S)-3-hydroxy-γ-butyrolactone from ethyl 4-chloro-3-hydroxybutyrate [see, e.g., Tetrahedr. Asym. 11. 3109-3112 (1996)]. However, such biological processes are not successful in terms of enzyme stability. Also, they cannot be regarded as industrially advantageous because complicated procedures are required to prepare substrates.